Abstract: The bevel shape of the SAWL pipe during joint-welding is analyzed. It is summarized that the improper root face angle is the root cause for the joint gap. Accordingly，the calculation formula for the root face angle is provided，while how the defective peaking influences the joint gap is discussed. Relevant suggestion is put forward for preventing occurrence of the joint gap. The analysis leads to such a conclusion that the joint gap as developed during pre-welding process is expected to be improved，and thus get the percentage of defects like porosity and burnthough， etc. as occurred during internal welding operation reduced to 5% or less by means of properly selecting root face angle，and appropriately adjusting the peaking value and the bevel dimensions as well.